1. Field of Invention
The present invention relates to incandescent light bulbs, particularly of a type having improved luminous efficacy.
2. Prior Art
Previous efforts at attaining significantly improved luminous efficacy in ordinary incandescent light bulbs--i.e., light bulbs of a type useful as direct replacements for present 120 Volt household light bulbs--have been directed toward the use of a reflector means operative to reflect much of the infrared radiation back onto the incandescent filament while letting visible radiation pass through with little attenuation.
Examples of approaches of this nature are provided by numerous prior art references, such as the following U.S. Pat. Nos.: No. 1,342,894 to Bugbee; No. 1,425,967 to Hoffman; No. 2,859,369 to Williams et al.; No. 4,039,878 to Eijkelenboom et al.; No. 4,160,929 to Thorington et al.; No. 4,283,653 to Brett; No. 4,366,407 to Walsh; and No. 4,375,605 to Fontana et al.
However, even though the basic principle has been known for decades, and even though the attainable efficacy improvement is on the order of several hundred percent, household light bulbs based on this principle of selective reflection of infrared energy is not yet available on the market. The reason for this is apparently connected with the difficulty in translating the basic principle into high-volume production of corresponding cost-effective household light bulbs.